This invention relates to an electromechanical valve actuator and more particularly, to an electromechanical valve actuator having integrated air cushioning pistons or assemblies which are effective to selectively decelerate the moving components of the actuator as they approach their respective seats, thereby providing a xe2x80x9csoft landingxe2x80x9d for the components and substantially reducing or eliminating hammering effects and noise and vibration harshness (xe2x80x9cNVHxe2x80x9d).
Valve actuator assemblies and systems are used in internal combustion engines in order to open and close the engine""s intake and/or exhaust valves. Prior valve timing systems typically include one or more camshafts which selectively engage the valves thereby causing the valves to open and close according to a certain timing sequence or strategy. Efforts have been made to increase the efficiency of vehicle engines and reduce emissions by eliminating the camshafts and operating the intake and exhaust valves by use of selectively controllable electromagnetic or electromechanical valve actuators.
Electromechanical valve actuators allow for independent control of the valve timing with respect to the vehicle""s crankshaft. This independence allows for optimization of the exhaust and intake valve timing events at all engine operating conditions. Controlling the intake valve events can eliminate the need for throttling the engine, which can provide a significant reduction in fuel consumption. Optimizing valve timing over the engine speed range can provide a xe2x80x9cflatterxe2x80x9d and more efficient torque curve than is possible with a conventional cam system, which is a compromise between xe2x80x9clow RPMxe2x80x9d and xe2x80x9chigh RPMxe2x80x9d operation. Other advantages of the electromechanical valve actuators and camless systems include the elimination of external xe2x80x9cEGRxe2x80x9d and throttling subsystems, enabling of Drive by Valve (xe2x80x9cDBVxe2x80x9d) systems which provide a fast response for torque demand, the selective activation and deactivation of individual cylinders in a variable displacement engine (deactivation of individual cylinders), and the valve timing of a Miller cycle engine.
A typical electromagnetic or electromechanical valve includes a closing magnetic coil, an opening magnetic coil, an armature, and two substantially identical springs. When the coils are de-energized, the two springs are compressed equally and the armature resides xe2x80x9cmidwayxe2x80x9d between the coils. In order to open the valve, the opening coil is energized, thereby attracting the armature and holding the valve in an open position. In order to close the valve, the holding current to the opening coil is xe2x80x9cswitched offxe2x80x9d and the valve spring force accelerates the valve toward its seat. At the midpoint of travel, the spring forces change direction and decelerate the valve. In order to assure that the valve will seat, the closing coil is energized and pulls the armature upward, thereby closing the valve.
Controlling the valve velocity as it contacts its seat (i.e., the xe2x80x9cseating velocityxe2x80x9d) is important to ensure smooth valve operation. Particularly, if the seating velocity is not reduced to achieve a relatively soft landing, the impact can result in a xe2x80x9chammering effectxe2x80x9d which can cause an unacceptable level of NVH and increased degradation of the actuator, valves, and valve seats. Controlling the valve velocity during valve opening events is similarly important for similar reasons. Particularly, it is important to reduce the velocity of the valve as it opens to soften the impact of components of the valve actuator against each other which occurs when the valve is fully opened.
There is therefore a need for a new and improved electromechanical or electromagnetic valve actuator which includes cushioning assemblies or devices which soften the landing of the valve actuating components and substantially reduce xe2x80x9chammering effectsxe2x80x9d and NVH.
A first non-limiting advantage of the invention is that it provides an electromagnetic or electromechanical valve actuator which substantially reduces NVH during opening and closing events.
A second non-limiting of the invention is that it includes one or more integrated cushioning pistons or assemblies which are effective to selectively decelerate the moving components of the actuator as they approach their respective seats, thereby providing a xe2x80x9csoft landingxe2x80x9d for the components and substantially reducing or eliminating hammering effects and noise vibration harshness.
According to a first aspect of the present invention, an electromagnetic actuator is provided for use in opening and closing a cylinder valve having a shaft. The actuator includes a closing coil; an opening coil; an armature which is coupled to the shaft of the valve and which is disposed between the closing coil and the opening coil; a housing which is coupled to the closing coil; and a pneumatic damper which is contained within the housing and which is effective to decelerate the valve during a valve closing event.
According to a second aspect of the present invention, a method is provided for reducing noise and vibration harshness in a electromechanical valve actuator of the type which selectively opens and closes a cylinder valve having a shaft. The method includes the steps of providing a housing having an internal bore; providing a piston; attaching the piston to the shaft of the valve; and causing the piston to be slidably disposed within the internal bore, effective to provide a deceleration force to the valve during a valve closing event.
These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings.